1. Field of the Invention
The present invention relates to an image recording apparatus, specifically to an image recording apparatus that does not require the use of an expensive memory with a large storage capacity, and one that can be connected to various image information sources with different transmission speeds.
2. Description of the Prior Art
Various types of image recording apparatuses that employ raster scanning using a laser beam have been proposed and are being put into practical use.
In this type of image recording apparatus, the image information from an image information source like image processing devices, such as an image scanner, video machine, television, computer, etc., is received in the form of an electrical signal. A laser beam modulated by the image information is reflected and deflected along a main scanning direction by an optical deflector. An image corresponding to the deflected laser beam is formed on a recording material that is transported and scanned along a subscanning direction that is generally perpendicular to the aforementioned main scanning direction. By this, the recording material is exposed to perform image recording by raster scanning method.
In this type of image recording apparatus, a storage unit such as a buffer memory is provided for storing the image information transmitted from the aforementioned image information source. One recording block, for example, a block containing a number of pages of image or a quantity of image information corresponding to one sheet or one page, is stored beforehand in this memory, and image recording is performed based on the image information stored in the memory.
In this case, in order to obtain a good image free from uneveness in densities and colors the process of image recording is performed as in the following: The light beam must be made to scan the recording material along the main scanning direction at a constant speed by making the optical deflector rotate continuously at an accurately constant speed. The optical deflector must be driven by a highly precise driver having small fluctuation in the speed of rotation. Also, the aforementioned light beam must be made to scan the recording material at a constant speed by making the aforementioned recording material move along the subcanning direction continuously at a constant speed. By the process described above, the recording material is exposed two-dimensionally.
However, even in this image recording apparatus employing the raster scanning method, image recording that produces high-quality pictures with high-gradation is still desired. In order to perform the recording of the equivalent of only one page of high quality image, the number of rasters becomes large and, consequently, the amount of image information required to record one page of high-quality image becomes large. Because of this, the speed of transmission of the image information from the image information source becomes slow relative to the recording speed of the image recording apparatus.
Therefore, in order to obtain a picture of good quality as mentioned above, image recording must be performed at a constant main scanning speed and a constant subscanning speed, the subscanning operation being performed continuously without interruption. To realize this, it is required that at least one page of image information transmitted from the image information source is first stored in a memory such as a buffer memory. The image information is then read from this memory and recording of the image on a recording material is performed.
However, usually for image information, even for monochrome images, one bit of information is needed for one pixel and, for one page of image information, a memory with a large storage capacity is required. Consequently, the image recording apparatus inevitably becomes expensive.
Further, for full color images, 8 bits of information is needed for one color per pixel; for the three colors R, G, and B, 24 bits of information is needed. Thus, a very large memory is required. Consequently, the same problem arises in that the image recording apparatus becomes very expensive.
Also, as mentioned earlier, this type of image recording apparatus is connected to various image information sources and image recording is performed based on the image information transmitted from these sources. Generally, the speed of transmission of the image information is different depending on the image information source. Consequently, because of the relation of the storage capacity of the memory and the image recording speed, a large number of varied image information sources with widely varying image information transmission speeds may not be connected to the same image recording apparatus.